1. Field
The presently disclosed subject matter relates to a fluorescent lamp, and more particularly to a cold cathode fluorescent lamp which, in at least one embodiment, can be used as a light source for a back light unit of a liquid crystal display mounted in a television, a personal computer, display devices, and the like.
2. Description of the Related Art
In a liquid crystal display (LCD) using office automation equipment such as a personal computer, a printer and the like, a backlight unit is mounted on the back of the LCD in order to facilitate visualization of the LCD. A cold cathode fluorescent lamp (CCFL) is frequently used as a light source for the backlight unit. In general, fluorescent lamps can be broadly classified into CCFL and hot cathode fluorescent lamp (HCFL) type lamps. A reason why the CCFL is frequently used as a light source for the backlight unit is that the CCFL generates a small amount of heat and enjoys low power consumption.
Fluorescent lamps that are classified into CCFL and HCFL type lamps can be broadly composed of an electrode unit and a tube unit. For example, an electrode unit of a CCFL is generally composed of an electrode, a stem lead and a lead wire. Materials used to make the electrode include nickel, however, in recent years niobium, molybdenum, tungsten, etc., have been used. Because the stem lead is generally sealed with a bead made by glass and/or the like, it can be made from kovar™ (a nickel-cobalt ferrous alloy), tungsten, molybdenum, etc., for which thermal expansion behavior is similar to that of glass. The lead wire for connecting to outside parts can be a dumet wire or a nickel wire, etc.
Each connecting portion of the above described components can be connected with a weld such as a resistance weld, a laser weld, and the like, and their components can be assembled as the electrode unit. The tube unit is generally formed as a glass tube, which can be approximately 2 mm in outside diameter and from 10 mm to 1,000 mm in length, and can be coated with a phosphor on an inner surface thereof. The glass tube of the tube unit can be sealed along with the stem lead by the above-described glass bead.
Various components for a fluorescent lamp having high brightness and long life and a fluorescent lamp using these components are generally known. For example, Patent Document No. 1 (Japanese Patent No. 2792543) discloses an electrode for a fluorescent lamp that provides high power and long life by inhibiting an effect of spattering. In addition, Patent Document No. 2 (Japanese Patent Application Laid Open JP2005-285587) discloses an electrode for a CCFL that provides long life and high power by preventing a blackening on an inner surface of a glass tube.
Furthermore, Patent Document No. 3 (Japanese Patent Application No. 2007-051078) discloses a fluorescent lamp that provides long life and high reliability by including an emitter electrode configured with a crystalline silicon carbide material having an electrical conductivity. The electrode units including the above emitter electrode can prevent blackening on an inner surface of the tube by avoiding the occurrence of spattering.
The above-referenced Patent Documents are listed below and are incorporated herein by reference.    1. Patent Document No. 1: Japanese Patent No. 2792543    2. Patent Document No. 2: Japanese Patent Application Laid Open JP2005-285587    3. Patent Document No. 3: Japanese Patent Application No. 2007-051078
Recently, televisions and the like have been provided with LCD units including a backlight unit which requires longer life and higher brightness than that of office automation equipment, such as personal computers and the like. Thus, the CCFL that is used as a light source for the backlight unit mounted on the back of the LCD should have a longer life and higher brightness than the conventional CCFL. In addition, because television screens are getting larger and larger, the size of the CCFL is also becoming longer and the operating voltage is also becoming high.
The life of the conventional CCFL will now be described. A main factor that determines the life of a CCFL is blackening on an inner surface of glass tube near the electrode unit. The blackening on the inner surface can be caused by several factors, including: having electrode matter beaten out from the surface of the electrode due to the presence of mercury ions and/or the like; material, such as the electrode matter material, adhering on the inner surface of the glass tube near the electrode unit; and material, such as the electrode matter material, blackening the inner surface of the glass tube. The above-described blackening can cause a reduction of the life of the CCFL.
In order to prevent this blackening, molybdenum and tungsten that advantageously prevent spatter of mercury ions have been employed as the electrode material in place of nickel. However, because blackening cannot be adequately prevented even if molybdenum and/or tungsten are used as the electrode material, there is a problem in that a favorable life may not be obtained.
On the other hand, electrodes that add a relatively small amount of material having a low work function, such as a lanthanum and the like, to the molybdenum or tungsten have been proposed. In addition, a molybdenum electrode or tungsten electrode that includes 4 wt % to 10 wt % of at least one or more than one of lanthanum oxide, yttrium oxide, cerium oxide, strontium oxide, hafnium oxide and barium oxide and 0.05 wt % to 0.5 wt % in a weight ratio of at least one or more than one of nickel, cobalt and palladium has also been proposed. However, there is a problem in that these electrodes may not meet the life requirements of the CCFL, because the life of the CCFL which is used as a light source for the LCD backlight unit of a television and the like should be long.
Furthermore, the CCFL according to Patent Document No. 3 can provide long life and high reliability by including an emitter electrode configured with a crystalline silicon carbide material having an electrical conductivity. However, the crystalline silicon carbide material may not be easily formed into a large size wafer at low cost and with high quality in the present circumstances.
The disclosed subject matter has been devised to consider the above and other features, problems and characteristics. Thus, embodiments of the disclosed subject matter can include a fluorescent lamp with a simple electrode structure that can prevent blackening on an inner surface of the lamp tube and therefore can meet various requirements for a longer life, higher brightness and the like. In addition, the disclosed subject matter can include a CCFL having a relatively long life, high brightness and high reliability. More specifically, certain embodiments of the disclosed subject matter can provide a CCFL having a long life in which a decrease of brightness can be maintained at less than 50% as compared to the initial value of brightness even after continuous emission for 60,000 hours.